The invention relates to a device for controlling the intensity and hue of illuminating light introduced through an optical fiber bundle of an endoscope for illuminating a part of a human body. More particularly, the invention relates to a device in which the mechanism and arrangement for illuminating light control is simplified and the light intensity control range is relatively large.
In observing a deep part of a body cavity or in photographing such with an endoscope of the general type to which the invention relates, it is necessary to illuminate the part to be examined with light introduced through the optical bundle of the endoscope. In photographing the body cavity being examined, the intensity of light thus introduced should be relatively high for the picture to have satisfactory detail. However, for observing the body cavity with the eye for relatively long periods of time, it is undesirable that the light have such a high intensity as it will thermally stimulate the body cavity.
In view of this, an illuminating light intensity control device has been previously employed in which, in observing the body cavity with the naked eye, an optical filter is inserted in the illuminating light path while for photographing the body cavity, the optical filter is retracted from the illuminating light path. In such an illuminating light intensity control device, the timing of the optical filter going in and out of the light path is made synchronous with the operation of the shutter in the photographing operation in order to minimize the thermal stimulus to the body cavity due to the high intensity light. Therefore, the illuminating light intensity control means is necessarily intricate in arrangement.
Moreover, for observing the body cavity with the naked eye, if the surface being observed is excessively bright, then the operator's eye may be dazzled, the contrast of the part being observed is lowered and, accordingly, it is difficult to satisfactorily observe the minute affected part of the body cavity. Thus, it is desirable that the intensity of the illuminating light be controlled according to the position and condition of a part to be examined of the body cavity. In the case where an incandescent lamp is employed as the light source, the intensity of illuminating light can be controlled over a relatively wide range by a light control device such as a voltage control device. However, in this case also, the light intensity range is limited because color hue at light emitted from an incandescent is affected by the reduction of the light intensity. Especially in the case where a discharge lamp is employed as the light source, the electric power control range is limited because the discharge lamp will properly emit light only over a relatively narrow range of input power so that the illuminating light intensity control range is correspondingly very narrow.
In order to be practical and suitable for actual clinical use, a device which is employed to vary the illuminating light intensity of an incandescent lamp should cause the color hue rendering to be satisfactory and a device used with a discharge lamp should be capable of varying the output intensity over a wide range.
Sometimes locating and observing an affected part of the body cavity can be readily achieved by changing the hue of the illuminating light according to the conditions of the affected part. Therefore, it is desirable that the control device be capable of hue control as well as intensity control.
In view of the foregoing, an object of the invention model is to provide an illumination light control device for an endoscope which can effectively control the intensity and hue of illuminating light and is simple in construction.